1. Field of the Invention
The present invention relates to an inkjet printing apparatus for printing an image by using a print head capable of ejecting ink and a method for controlling the inkjet printing apparatus.
2. Description of the Related Art
An inkjet printing apparatus prints an image on a print medium by ejecting ink, which is a printing agent, from a plurality of ejection ports formed on a print head. As for the print head used in the inkjet printing apparatus, there is known a print head in which an ejection energy generation element, such as an electrothermal transducer or an electromechanical transducer, is arranged in a liquid path that is in communication with the ejection ports, and the ejection energy causes ink in the liquid path to be ejected from the ejection ports. Some of the inks used for printing use water as a solvent, and when exposed to the air, the water serving as the solvent evaporates to cause an increase in viscosity (thickening of the ink). If the viscosity of the ink in the print head increases, the ejection of the ink during the printing operation becomes unstable, leading to a decrease in image quality. Accordingly, the currently used inkjet printing apparatus performs ink discharge processing to discharge the thickened ink or the ink containing dust or the like from the print head before printing an image.
Further, the inkjet printing apparatus is provided with a capping portion for covering (capping) an ejection port surface on which the ejection ports of the print head are formed as a configuration of preventing the ink in the print head from thickening during ejection standby in which a printing operation is not performed. However, the capping portion is often shared as an ink accepting member for accepting the thickened ink discharged from the print head due to the limit of the body size of the inkjet printing apparatus. Therefore, a capping portion needs to have a capacity for accepting the discharged ink, and accordingly a predetermined shielded space which is shielded from outside air is formed between the ejection port surface of the print head and the capping portion in a state in which the print head is capped. This causes the ejection ports to be in contact with air in the shielded space even after the capping, and the ink near the ejection ports is occasionally thickened. In addition, after capping the print head and depending on hermeticity of the capping portion, water may gradually evaporate over time to the outside of the capping portion. This may promote the thickening of the ink.
To reduce the thickening of the ink after the capping, Japanese Patent Laid-Open No. 2004-181844 discloses a technique of providing a printing apparatus body and a print head with a humidity sensor to regularly predict a humidity inside a capping portion and performing ejection to the capping portion the number of times corresponding to the predicted humidity.
In the technique disclosed in Japanese Patent Laid-Open No. 2004-181844, however, the ejection continues according to the humidity, and therefore the volume of ink to be discarded increases.